I’ve never tried an Xjet for roof washing but sounds interesting. If you use straight 12% SH with the Xjet, I would think this would work. There are videos online with people doing it. You should get a 3-1 mix with an 8 gpm machine without any proportioners which gives you 4% SH. You might have to go over some spots twice if that’s not hot enough but I usually start at 4% for most roofs. Also, you can use an Xjet with a lower GPM machine and get an even hotter mix. You’ll just need to make sure you use a separate water hose for spraying down the plants, etc. And most importantly, don’t take my advice with roof washing. Always test test test!